U.S. patent application number 15/510741 was filed with the patent office on 2017-09-28 for reference signal transmission method in multi-antenna wireless communication system, and apparatus therefor.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Jiwon KANG, Kijun KIM, Kitae KIM, Youngtae KIM, Jonghyun PARK.
Application Number | 20170279501 15/510741 |
Document ID | / |
Family ID | 55581505 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170279501 |
Kind Code |
A1 |
KIM; Youngtae ; et
al. |
September 28, 2017 |
REFERENCE SIGNAL TRANSMISSION METHOD IN MULTI-ANTENNA WIRELESS
COMMUNICATION SYSTEM, AND APPARATUS THEREFOR
Abstract
The present invention relates to a base station in a wireless
communication system which supports multi-antennas with multiple
horizontal domains and multiple vertical domains. Particularly, the
present invention comprises: a radio frequency unit and a
processor, wherein the radio frequency unit comprises a first radio
frequency (RF) chain and a second radio frequency (RF) chain which
are connected to antenna elements corresponding to multiple
vertical antennas with specific horizontal domains, wherein the
processor, connected to the radio frequency unit, is configured to
transmit reference signals, and wherein the first RF chain and the
second RF chain are configured for different reference signals.
Inventors: |
KIM; Youngtae; (Seoul,
KR) ; KIM; Kijun; (Seoul, KR) ; KANG;
Jiwon; (Seoul, KR) ; PARK; Jonghyun; (Seoul,
KR) ; KIM; Kitae; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
55581505 |
Appl. No.: |
15/510741 |
Filed: |
September 25, 2015 |
PCT Filed: |
September 25, 2015 |
PCT NO: |
PCT/KR2015/010180 |
371 Date: |
March 13, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62055625 |
Sep 25, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 5/0023 20130101;
H04L 5/0005 20130101; H04B 7/0413 20130101; H04L 5/0035 20130101;
H04L 5/0073 20130101; H04W 4/18 20130101; H04B 7/06 20130101; H04L
5/005 20130101; H04B 7/0469 20130101 |
International
Class: |
H04B 7/0413 20060101
H04B007/0413; H04L 5/00 20060101 H04L005/00; H04B 7/06 20060101
H04B007/06; H04W 4/18 20060101 H04W004/18 |
Claims
1. A base station in a wireless communication system supporting
multiple antennas having a plurality of horizontal domains and a
plurality of vertical domains, comprising: an RF (radio frequency)
unit; and a processor, wherein the RF unit comprises a first RF
chain and a second RF chain which are connected with antenna
elements corresponding to a plurality of vertical antennas having a
specific horizontal domain, wherein the processor connected with
the RF unit is configured to transmit reference signals, and
wherein the first RF chain and the second RF chain are configured
for reference signals different from each other.
2. The base station of claim 1, wherein the first RF chain is
configured to be used for a DMRS (de-modulation reference signal)
port and wherein the second RF chain is configured to be used for
at least one of a CSI RS (channel state information-reference
signal) port and a CRS (cell-specific reference signal) port.
3. The base station of claim 1, wherein a CSI-RS and a CRS are
configured to be transmitted using a different time resource.
4. The base station of claim 1, wherein the RF unit further
comprises a third RF chain, wherein the first RF chain is used for
a DMRS (de-modulation reference signal) port, wherein the second RF
chain is used for a CSI RS (channel state information-reference
signal) port, and wherein the third RF chain is used for a CRS
(cell-specific reference signal) port.
5. The base station of claim 1, wherein the RF unit is associated
with the first RF chain, associated with a plurality of first phase
shifters respectively corresponding to a plurality of the antenna
elements and the second RF chain, and configured to contain a
plurality of second phase shifters respectively corresponding to a
plurality of the antenna elements.
6. A method of transmitting a reference signal, which is
transmitted by a base station in a wireless communication system
supporting multiple antennas having a plurality of horizontal
domains and a plurality of vertical domains, comprising the steps
of: signaling a CSI-RS (channel state information-reference signal)
configuration that indicates whether to apply CDM (code division
multiplexing); mapping a CSI-RS (channel state
information-reference signal) sequence to REs (resource elements)
based on an antenna port; and if the CSI-RS configuration indicates
not to apply the CDM, transmitting a channel state
information-reference signal of which TDM (time division
multiplexing) and FDM (frequency division multiplexing) are applied
to the mapped resource element to a user equipment.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more particularly, to a method of transmitting a
reference signal in a wireless communication system supporting
multiple antennas and an apparatus therefor.
BACKGROUND ART
[0002] MIMO (multi-input multi-output) technology means a method of
improving data transceiving efficiency by adopting multiple
transmitting antennas and multiple receiving antennas instead of a
single transmitting antenna and a single receiving antenna. In
particular, this technology increases capacity or enhances
performance using multiple antennas in a transmitting or receiving
end of a wireless communication system. This MIMO technology may be
called multi-antenna technology.
[0003] In order to support MIMO transmission, it may be able to use
a precoding matrix to appropriately distribute transmission
information to each antenna in accordance with a channel status and
the like. In the conventional 3GPP (3.sup.rd generation partnership
project) LTE (long term evolution) system, maximum 4 transmitting
antennas are supported for downlink transmission and a
corresponding precoding codebook is defined.
[0004] In a multi-antenna system-based cellular communication
environment, data transfer rate can be enhanced via beamforming
between a transmitting end and a receiving end. Whether to apply a
beamforming scheme is managed based on channel information. In
general, it may be able to use a scheme that a receiving end
appropriately quantizes a channel estimated by a reference signal
and the like using a codebook and gives a transmitting end feedback
on the quantized channel.
[0005] In the following, a spatial channel matrix (simply, channel
matrix) capable of being used for generating a codebook is briefly
explained. The spatial channel matrix (or, channel matrix) can be
represented as follows.
H ( i , k ) = [ h 1 , 1 ( i , k ) h 1 , 2 ( i , k ) h 1 , Nt ( i ,
k ) h 1 , 2 ( i , k ) h 2 , 2 ( i , k ) h 2 , Nt ( i , k ) h Nr , 1
( i , k ) h Nr , 2 ( i , k ) h Nr , Nt ( i , k ) ] ##EQU00001##
[0006] In this case, H (i, k) corresponds to a spatial channel
matrix, Nr corresponds to the number of reception antennas, Nt
corresponds to the number of transmission antennas, r corresponds
to an index of an reception antenna, t corresponds to an index of a
transmission antenna, i corresponds to an index of an OFDM (or
SC-FDMA) symbol, and k corresponds to an index of a subcarrier.
[0007] h.sub.r,t(i,k) corresponds to an element of a channel matrix
H (i, k) indicating a state of an r.sup.th channel and a t.sup.th
antenna on an i.sup.th symbol and k.sup.th subcarrier.
[0008] A spatial channel covariance matrix capable of being used in
the present invention is briefly explained in the following. The
spatial channel covariance matrix can be represented by such a sign
as R. In particular, the spatial channel covariance matrix can be
represented as R=E[H.sub.i,k.sup.HH.sub.i,k]. In this case, H and R
correspond to a spatial channel matrix and a spatial channel
covariance matrix, respectively. E[ ] corresponds to a mean, i
corresponds to a symbol index, and k corresponds to a frequency
index.
[0009] SVD (singular value decomposition) is one of important
methods for decomposing a rectangular matrix. The SCD is widely
used in signal processing and statistics. The SVD generalizes a
spectrum theory of a matrix in response to a random rectangular
matrix. An orthogonal square matrix can be decomposed to a diagonal
matrix using the spectrum theory based on an Eigen value. Assume
that a channel matrix H corresponds to m.times.n matrix consisting
of a set element of real numbers or complex numbers. In this case,
the matrix H can be represented by multiplication of three matrixes
described in the following.
H.sub.m.times.n=U.sub.m.times.m.SIGMA..sub.m.times.nV.sub.n.times.n.sup.-
H
[0010] In this case, U and V correspond to unitary matrixes and
.SIGMA. corresponds to m.times.n diagonal matrix including a
singular value which is not a negative value. The singular value
corresponds to .SIGMA.=diag(.sigma..sub.1 . . .
.sigma..sub.r),.sigma..sub.i= {square root over (.lamda..sub.i)}.
As mentioned above, when a matrix is represented by multiplication
of three matrixes, it is referred to as singular value
decomposition. It may be able to handle a much more general matrix
using the singular value decomposition compared to Eigen value
decomposition capable of decomposing an orthogonal square matrix
only. The singular value decomposition and the Eigen value
decomposition are related to each other.
[0011] When a matrix H corresponds to a Hermite matrix which is
positive definite, all Eigen values of the H correspond to real
numbers which are not negative numbers. In this case, a singular
value and a singular vector of the H correspond to real numbers
which are not negative numbers. In particular, the singular value
and the singular vector of the H become identical to the Eigen
value and the Eigen vector of the H. Meanwhile, EVD (Eigen value
Decomposition) can be represented as follows (in this case, Eigen
value may correspond to .lamda.1, . . . , .lamda.r).
HH.sup.H=(U.SIGMA.V.sup.H)(U.SIGMA.V.sup.H).sup.H=U.SIGMA..SIGMA..sup.TU-
.sup.H
H.sup.HH=(U.SIGMA.V.sub.H).sup.H(U.SIGMA.V.sup.H).sup.H=V.SIGMA..sup.T.S-
IGMA.V
[0012] In this case, Eigen value may correspond to .lamda.1, . . .
, .lamda.r. When singular value decomposition is performed on
HH.sup.H, it is able to know information on U among U and V that
indicate channel direction. When singular value decomposition is
performed on H.sup.HH, it is able to know information on V. In
general, each of a transmitting end and a receiving end performs
beamforming to achieve a higher transfer rate in MU-MIMO (multi
user-MIMO). If a beam of the receiving end and a beam of the
transmitting end are represented by a matrix T and a matrix W,
respectively, a channel to which beamforming is applied can be
represented as THW=TU(.SIGMA.)VW. Hence, it may be preferable to
generate a reception beam on the basis of the U and generate a
transmission beam on the basis of the V to achieve a higher
transfer rate.
[0013] In general, main concern in designing a codebook is to
reduce feedback overhead using the number of bits as small as
possible and precisely quantify a channel to achieve sufficient
beamforming gain. One of schemes of designing a codebook, which is
proposed or selected by recent communication standard such as 3GPP
LTE (3rd Generation Partnership Project Long Term Evolution),
LTE-Advanced, IEEE 16m system, etc. corresponding to an example of
a mobile communication system, is to transform a codebook using a
long-term covariance matrix of a channel as shown in equation 1 in
the following.
W'=norm(RW) [Equation 1]
[0014] In this case, W corresponds to a legacy codebook for
reflecting short-term channel information, R corresponds to a
long-term covariance matrix of a channel H, and norm (A)
corresponds to a normalized matrix that norm is normalized by 1
according to each column of a matrix A. W' corresponds to a final
codebook transformed from the legacy codebook W using the channel
matrix H, the long-term covariance matrix R of the channel matrix H
and a norm function.
[0015] The R, which is the long-term covariance matrix of the
channel matrix H, can be represented as equation 2 in the
following.
R = E [ H H H ] = V .LAMBDA. V H = i = 1 Nt .sigma. i v i v i H [
Equation 2 ] ##EQU00002##
[0016] In this case, if the singular value decomposition is
performed on the R, which is the long-term covariance matrix of the
channel matrix H, the R is decomposed to V.LAMBDA.V.sup.H. V
corresponds to Nt.times.Nt unitary matrix and has Vi as an i.sup.th
column vector. .LAMBDA. corresponds to a diagonal matrix and has
.sigma..sub.i as an i.sup.th diagonal component. V.sup.H
corresponds to an Hermitian matrix of the V. And,
.sigma..sub.i,v.sub.i respectively correspond to an i.sup.th
singular value and an i.sup.th singular column vector corresponding
to the i.sup.th singular value
(.sigma..sub.1.gtoreq..sigma..sub.2.gtoreq. . . .
.gtoreq..sigma..sub.Nt).
DISCLOSURE OF THE INVENTION
Technical Task
[0017] A technical task of the present invention is to provide a
method of transmitting a reference signal in a multi-antenna
wireless communication system and an apparatus therefor.
[0018] It will be appreciated by persons skilled in the art that
the objects that could be achieved with the present invention are
not limited to what has been particularly described hereinabove and
the above and other objects that the present invention could
achieve will be more clearly understood from the following detailed
description.
Technical Solution
[0019] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described, according to one embodiment, a base station in a
wireless communication system supporting multiple antennas having a
plurality of horizontal domains and a plurality of vertical domains
includes an RF (radio frequency) unit and a processor. In this
case, the RF unit includes a first RF chain and a second RF chain
which are connected with antenna elements corresponding to a
plurality of vertical antennas having a specific horizontal domain,
the processor connected with the RF unit is configured to transmit
reference signals, and the first RF chain and the second RF chain
are configured for reference signals different from each other.
[0020] Preferably, the first RF chain is configured to be used for
a DMRS (de-modulation reference signal) port and the second RF
chain is configured to be used for at least one of a CSI RS
(channel state information-reference signal) port and a CRS
(cell-specific reference signal) port.
[0021] Preferably, a CSI-RS and a CRS are configured to be
transmitted using a different time resource.
[0022] Preferably, the RF unit further includes a third RF chain,
the first RF chain is configured to be used for a DMRS
(de-modulation reference signal) port, the second RF chain is
configured to be used for a CSI RS (channel state
information-reference signal) port, and the third RF chain is
configured to be used for a CRS (cell-specific reference signal)
port.
[0023] Preferably, the RF unit is associated with the first RF
chain, associated with a plurality of first phase shifters
respectively corresponding to a plurality of the antenna elements
and the second RF chain, and configured to contain a plurality of
second phase shifters respectively corresponding to a plurality of
the antenna elements.
[0024] To further achieve these and other advantages and in
accordance with the purpose of the present invention, according to
a different embodiment, a method of transmitting a reference
signal, which is transmitted by a base station in a wireless
communication system supporting multiple antennas having a
plurality of horizontal domains and a plurality of vertical
domains, includes the steps of signaling a CSI-RS (channel state
information-reference signal) configuration that indicates whether
to apply CDM (code division multiplexing), mapping a CSI-RS
(channel state information-reference signal) sequence to REs
(resource elements) based on an antenna port, and if the CSI-RS
configuration indicates not to apply the CDM, transmitting a
channel state information-reference signal of which TDM (time
division multiplexing) and FDM (frequency division multiplexing)
are applied to the mapped resource element to a user equipment.
Advantageous Effects
[0025] According to embodiments of the present invention, it is
able to efficiently provide a method of transmitting a reference
signal in a multi-antenna wireless communication system.
[0026] It will be appreciated by persons skilled in the art that
that the effects achieved by the present invention are not limited
to what has been particularly described hereinabove and other
advantages of the present invention will be more clearly understood
from the following detailed description.
DESCRIPTION OF DRAWINGS
[0027] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0028] FIG. 1 is a diagram showing a network structure of an
Evolved Universal Mobile Telecommunications System (E-UMTS) as an
example of a mobile communication system;
[0029] FIG. 2 is a block diagram illustrating configurations of a
base station and a user equipment in a wireless communication
system according to the present invention;
[0030] FIG. 3 is a diagram for a configuration of a general MIMO
communication system;
[0031] FIG. 4 is a diagram for an example of a general CDD
structure in a MIMO system;
[0032] FIG. 5 is a diagram for explaining a basic concept of a
codebook-based precoding;
[0033] FIG. 6 is a diagram for examples of configuring 8
transmission antennas;
[0034] FIG. 7 is a diagram for an active antenna system (AAS);
[0035] FIGS. 8 and 9 are diagrams for structures of an antenna
element and a radio frequency chain to perform beamforming for
2D-AAS in a legacy system;
[0036] FIGS. 10 and 11 are diagrams for structures of an antenna
element and a radio frequency chain to perform beamforming for
2D-AAS according to the present invention;
[0037] FIG. 12 is a diagram for CSI-RS mapping in LTE system;
[0038] FIG. 13 is a diagram for a case of performing mapping by
modifying CSI-RS according to the present invention.
BEST MODE
Mode for Invention
[0039] Hereinafter, the preferred embodiments of the present
invention will be described with reference to the accompanying
drawings. It is to be understood that the detailed description,
which will be disclosed along with the accompanying drawings, is
intended to describe the exemplary embodiments of the present
invention, and is not intended to describe a unique embodiment with
which the present invention can be carried out. The following
detailed description includes detailed matters to provide full
understanding of the present invention. However, it will be
apparent to those skilled in the art that the present invention can
be carried out without the detailed matters. For example, the
following detailed description is given under the assumption that
3GPP LTE mobile communication systems are used. However, the
description may be applied to any other mobile communication system
except for specific features inherent to the 3GPP LTE systems.
[0040] In some cases, to prevent the concept of the present
invention from being ambiguous, structures and apparatuses of the
known art will be omitted, or will be shown in the form of a block
diagram based on main functions of each structure and apparatus.
Also, wherever possible, the same reference numbers will be used
throughout the drawings and the specification to refer to the same
or like parts.
[0041] Moreover, in the following description, it is assumed that a
terminal refers to a mobile or fixed type user equipment such as a
user equipment (UE), and an advanced mobile station (AMS). Also, it
is assumed that a base station refers to a random node of a network
terminal, such as Node B, eNode B, and an access point (AP), which
performs communication with the user equipment.
[0042] In a mobile communication system, a user equipment may
receive information from a base station through a downlink and
transmit information to the base station through an uplink. The
information that the user equipment transmits or receives includes
data and various types of control information. There are various
physical channels according to the types and usages of information
that the user equipment transmits or receives.
[0043] As an example of a mobile communication system to which the
present invention is applicable, a 3rd Generation Partnership
Project Long Term Evolution (hereinafter, referred to as LTE)
communication system is described in brief.
[0044] FIG. 1 is a view schematically illustrating a network
structure of an E-UMTS as an exemplary radio communication
system.
[0045] An Evolved Universal Mobile Telecommunications System
(E-UMTS) is an advanced version of a conventional Universal Mobile
Telecommunications System (UMTS) and basic standardization thereof
is currently underway in the 3GPP. E-UMTS may be generally referred
to as a Long Term Evolution (LTE) system. For details of the
technical specifications of the UMTS and E-UMTS, reference can be
made to Release 7 and Release 8 of "3rd Generation Partnership
Project; Technical Specification Group Radio Access Network".
[0046] Referring to FIG. 1, the E-UMTS includes a User Equipment
(UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located
at an end of the network (E-UTRAN) and connected to an external
network. The eNBs may simultaneously transmit multiple data streams
for a broadcast service, a multicast service, and/or a unicast
service.
[0047] One or more cells may exist per eNB. The cell is set to
operate in one of bandwidths such as 1.25, 2.5, 5, 10, 15, and 20
MHz and provides a downlink (DL) or uplink (UL) transmission
service to a plurality of UEs in the bandwidth. Different cells may
be set to provide different bandwidths. The eNB controls data
transmission or reception to and from a plurality of UEs. The eNB
transmits DL scheduling information of DL data to a corresponding
UE so as to inform the UE of a time/frequency domain in which the
DL data is supposed to be transmitted, coding, a data size, and
hybrid automatic repeat and request (HARQ)-related information.
[0048] In addition, the eNB transmits UL scheduling information of
UL data to a corresponding UE so as to inform the UE of a
time/frequency domain which may be used by the UE, coding, a data
size, and HARQ-related information. An interface for transmitting
user traffic or control traffic may be used between eNBs. A core
network (CN) may include the AG and a network node or the like for
user registration of UEs. The AG manages the mobility of a UE on a
tracking area (TA) basis. One TA includes a plurality of cells.
[0049] Although wireless communication technology has been
developed to LTE based on wideband code division multiple access
(WCDMA), the demands and expectations of users and service
providers are on the rise. In addition, considering other radio
access technologies under development, new technological evolution
is required to secure high competitiveness in the future. Decrease
in cost per bit, increase in service availability, flexible use of
frequency bands, a simplified structure, an open interface,
appropriate power consumption of UEs, and the like are
required.
[0050] Recently, 3GPP has standardized technology subsequent to
LTE. In this specification, the technology will be referred to as
"LTE-Advanced" or "LTE-A". A main difference between the LTE system
and the LTE-A system is a system bandwidth. The LTE-A system aims
to support a wideband of up to 100 MHz. To achieve this, the LTE-A
system employs carrier aggregation or bandwidth aggregation that
accomplishes a wideband using a plurality of frequency blocks.
Carrier aggregation uses a plurality of frequency blocks as a large
logical frequency band in order to achieve a wider frequency band.
The bandwidth of each frequency block can be defined on the basis
of a system block bandwidth used in the LTE system. Each frequency
block is transmitted using a component carrier.
[0051] FIG. 2 is a block diagram illustrating configurations of a
base station 205 and a user equipment 210 in a wireless
communication system 200.
[0052] Although one base station 205 and one user equipment 210 are
shown for simplification of a wireless communication system 200,
the wireless communication system 200 may include one or more base
stations and/or one or more user equipments.
[0053] Referring to FIG. 2, the base station 105 may include a
transmitting (Tx) data processor 215, a symbol modulator 220, a
transmitter 225, a transmitting and receiving antenna 230, a
processor 280, a memory 285, a receiver 290, a symbol demodulator
295, and a receiving (Rx) data processor 297. The user equipment
210 may include a Tx data processor 265, a symbol modulator 270, a
transmitter 275, a transmitting and receiving antenna 235, a
processor 255, a memory 260, a receiver 240, a symbol demodulator
255, and an Rx data processor 250. Although the antennas 230 and
235 are respectively shown in the base station 205 and the user
equipment 210, each of the base station 205 and the user equipment
210 includes a plurality of antennas. Accordingly, the base station
205 and the user equipment 210 according to the present invention
support a multiple input multiple output (MIMO) system. Also, the
base station 205 according to the present invention may support
both a single user-MIMO (SU-MIMO) system and a multi user-MIMO
(MU-MIMO) system.
[0054] Moreover, although it is not depicted in FIG. 2, an RF chain
corresponds to a part of which a filter and a power amp are
combined in an antenna. Specifically, the RF chain can include an
RF transmission chain and an RF reception chain. The RF
transmission chain includes a DAC (digital-to-analog converter), a
mixer for frequency up converting, a PA (power amplifier), a
duplexer, and a diplexer. The DAC converts a digital signal into an
analog signal in baseband. The mixer multiplies a baseband signal
by a carrier to convert the baseband signal into a band-pass
signal. The PA raises strength of the band-pass signal. The
duplexer plays a role of a filter to distinguish an uplink signal
from a downlink signal. The diplexer plays a role of a filter to
distinguish (operating) bands different from each other. The RF
reception chain includes a diplexer, a duplexer, an LNA (low noise
amplifier), a mixer for frequency down converting, and an ADC
(analog-to-digital converter). The LNA amplifies strength of a
radio signal which is attenuated in the course of transmission. The
mixer multiplies a band-pass signal by a carrier to covert the
band-pass signal into a baseband signal. The ADC converts an analog
signal into a digital signal in a baseband.
[0055] On a downlink, the Tx data processor 215 receives traffic
data, formats and codes the received traffic data, interleaves and
modulates (or symbol maps) the coded traffic data, and provides the
modulated symbols ("data symbols"). The symbol modulator 220
receives and processes the data symbols and pilot symbols and
provides streams of the symbols.
[0056] The symbol modulator 220 multiplexes the data and pilot
symbols and transmits the multiplexed data and pilot symbols to the
transmitter 225. At this time, the respective transmitted symbols
may be a signal value of null, the data symbols and the pilot
symbols. In each symbol period, the pilot symbols may be
transmitted continuously. The pilot symbols may be frequency
division multiplexing (FDM) symbols, orthogonal frequency division
multiplexing (OFDM) symbols, time division multiplexing (TDM)
symbols, or code division multiplexing (CDM) symbols.
[0057] The transmitter 225 receives the streams of the symbols and
converts the received streams into one or more analog symbols.
Also, the transmitter 225 generates downlink signals suitable for
transmission through a radio channel by additionally controlling
(for example, amplifying, filtering and frequency upconverting) the
analog signals. Subsequently, the downlink signals are transmitted
to the user equipment through the antenna 230.
[0058] In the user equipment 210, the antenna 235 receives the
downlink signals from the base station 205 and provides the
received signals to the receiver 240. The receiver 240 controls
(for example, filters, amplifies and frequency downcoverts) the
received signals and digitalizes the controlled signals to acquire
samples. The symbol demodulator 245 demodulates the received pilot
symbols and provides the demodulated pilot symbols to the processor
255 to perform channel estimation.
[0059] Also, the symbol demodulator 245 receives a frequency
response estimation value for the downlink from the processor 255,
acquires data symbol estimation values (estimation values of the
transmitted data symbols) by performing data demodulation for the
received data symbols, and provides the data symbol estimation
values to the Rx data processor 250. The Rx data processor 250
demodulates (i.e., symbol de-mapping), deinterleaves, and decodes
the data symbol estimation values to recover the transmitted
traffic data.
[0060] Processing based on the symbol demodulator 245 and the Rx
data processor 250 is complementary to processing based on the
symbol demodulator 220 and the Tx data processor 215 at the base
station 205.
[0061] On an uplink, the Tx data processor 265 of the user
equipment 210 processes traffic data and provides data symbols. The
symbol modulator 270 receives the data symbols, multiplexes the
received data symbols with the pilot symbols, performs modulation
for the multiplexed symbols, and provides the streams of the
symbols to the transmitter 275. The transmitter 275 receives and
processes the streams of the symbols and generates uplink signals.
The uplink signals are transmitted to the base station 205 through
the antenna 235.
[0062] The uplink signals are received in the base station 205 from
the user equipment 210 through the antenna 230, and the receiver
290 processes the received uplink signals to acquire samples.
Subsequently, the symbol demodulator 295 processes the samples and
provides data symbol estimation values and the pilot symbols
received for the uplink. The Rx data processor 297 recovers the
traffic data transmitted from the user equipment 210 by processing
the data symbol estimation values.
[0063] The processors 255 and 280 of the user equipment 210 and the
base station 205 respectively command (for example, control,
adjust, manage, etc.) the operation at the user equipment 210 and
the base station 205. The processors 255 and 280 may respectively
be connected with the memories 260 and 285 that store program codes
and data. The memories 260 and 285 respectively connected to the
processor 280 store operating system, application, and general
files therein.
[0064] Each of the processors 255 and 280 may be referred to as a
controller, a microcontroller, a microprocessor, and a
microcomputer. Meanwhile, the processors 255 and 280 may be
implemented by hardware, firmware, software, or their combination.
If the embodiment of the present invention is implemented by
hardware, application specific integrated circuits (ASICs), digital
signal processors (DSPs), digital signal processing devices
(DSPDs), programmable logic devices (PLDs), and field programmable
gate arrays (FPGAs) configured to perform the embodiment of the
present invention may be provided in the processors 255 and 280.
Meanwhile, if the embodiment according to the present invention is
implemented by firmware or software, firmware or software may be
configured to include a module, a procedure, or a function, which
performs functions or operations of the present invention. Firmware
or software configured to perform the present invention may be
provided in the processors 255 and 280, or may be stored in the
memories 260 and 285 and driven by the processors 255 and 280.
[0065] Layers of a radio interface protocol between the user
equipment 110 or the base station 105 and a wireless communication
system (network) may be classified into a first layer L1, a second
layer L2 and a third layer L3 on the basis of three lower layers of
OSI (open system interconnection) standard model widely known in
communication systems. A physical layer belongs to the first layer
L1 and provides an information transfer service using a physical
channel. A radio resource control (RRC) layer belongs to the third
layer and provides control radio resources between the user
equipment and the network. The user equipment and the base station
may exchange RRC messages with each another through the RRC
layer.
[0066] The term, base station used in the present invention may
refer to a "cell or sector" when used as a regional concept. A
serving base station (or serving cell) may be regarded as a base
station which provides main services to UEs and may transmit and
receive control information on a coordinated multiple transmission
point. In this sense, the serving base station (or serving cell)
may be referred to as an anchor base station (or anchor cell).
Likewise, a neighboring base station may be referred to as a
neighbor cell used as a local concept.
[0067] Multiple Antenna System
[0068] In the multiple antenna technology, reception of a message
does not depend on a single antenna path. Instead, in the multiple
antenna technology, data fragments received through multiple
antennas are collected and combined to complete data. If the
multiple antenna technology is used, a data transfer rate within a
cell region of a specific size may be improved, or system coverage
may be improved while ensuring a specific data transfer rate. In
addition, this technology can be broadly used by mobile
communication devices and relays. The multiple antenna technology
is getting a spotlight as a next generation technology capable of
overcoming restriction on mobile communication traffic.
[0069] FIG. 3(a) shows the configuration of a wireless
communication system including multiple antennas. As shown in FIG.
3(a), if the number of transmit (Tx) antennas and the number of Rx
antennas are respectively increased to N.sub.T and N.sub.R at the
same time, a theoretical channel transmission capacity of the MIMO
communication system increases in proportion to the number of
antennas, differently from the above-mentioned case in which only a
transmitter or receiver uses several antennas, so that transmission
rate and frequency efficiency can be greatly increased. In this
case, the transfer rate acquired by the increasing channel
transmission capacity can theoretically increase by a predetermined
amount that corresponds to multiplication of a maximum transfer
rate (Ro) acquired when one antenna is used and a rate of increase
(Ri). The rate of increase (Ri) can be represented by the following
equation 1.
R.sub.i=min(N.sub.T,N.sub.R) [Equation 1]
[0070] For example, provided that a MIMO system uses four Tx
antennas and four Rx antennas, the MIMO system can theoretically
acquire a high transfer rate which is four times higher than that
of a single antenna system. After the above-mentioned theoretical
capacity increase of the MIMO system was demonstrated in the
mid-1990s, many developers began to conduct intensive research into
a variety of technologies which can substantially increase data
transfer rate using the theoretical capacity increase. Some of the
above technologies have been reflected in a variety of wireless
communication standards, for example, third-generation mobile
communication or next-generation wireless LAN, etc.
[0071] A variety of MIMO-associated technologies have been
intensively researched by many companies or developers, for
example, research into information theory associated with MIMO
communication capacity under various channel environments or
multiple access environments, research into a radio frequency (RF)
channel measurement and modeling of the MIMO system, and research
into a space-time signal processing technology.
[0072] Mathematical modeling of a communication method for use in
the above-mentioned MIMO system will hereinafter be described in
detail. As can be seen from FIG. 3 (a), it is assumed that there
are N.sub.T Tx antennas and N.sub.R Rx antennas. In the case of a
transmission signal, a maximum number of transmission information
pieces is N.sub.T under the condition that N.sub.T Tx antennas are
used, so that the transmission information can be represented by a
specific vector shown in the following equation 4.
s=[s.sub.1,s.sub.2, . . . ,s.sub.N.sub.T].sup.T [Equation 4]
[0073] In the meantime, individual transmission information pieces
s.sub.1, s.sub.2, . . . , s.sub.NT may have different transmission
powers. In this case, if the individual transmission powers are
denoted by P.sub.1, P.sub.2, . . . , P.sub.NT, transmission
information having an adjusted transmission power can be
represented by a specific vector shown in the following equation
5.
s=.left brkt-bot.s.sub.1,s.sub.2, . . . ,s.sub.N.sub.T.right
brkt-bot..sup.T=[Ps.sub.1,Ps.sub.2, . . . ,Ps.sub.N.sub.T].sup.T
[Equation 5]
[0074] In Equation 5, s is a transmission vector, and can be
represented by the following equation 6 using a diagonal matrix P
of a transmission power.
s ^ = [ P 1 0 P 2 0 P N T ] [ s 1 s 2 s N T ] = Ps [ Equation 6 ]
##EQU00003##
[0075] In the meantime, the information vector s having an adjusted
transmission power is applied to a weight matrix W, so that N.sub.T
transmission signals x.sub.1, x.sub.2, . . . , x.sub.NT to be
actually transmitted are configured. In this case, the weight
matrix W is adapted to properly distribute transmission information
to individual antennas according to transmission channel
situations. The above-mentioned transmission signals x.sub.1,
x.sub.2, . . . , x.sub.NT can be represented by the following
equation 7 using the vector X. Here, W.sub.ij denotes a weight
between i-th Tx antenna and j-th information. W represents a weight
matrix or precoding matrix.
x = [ x 1 x 2 x i x N T ] = [ w 11 w 12 w 1 N T w 12 w 12 w 2 N T w
i 2 w i 2 w iN T w N T 1 w N T 2 w N T N T ] [ s ^ 1 s ^ 2 s ^ j s
^ N T ] = W s ^ = WPs [ Equation 7 ] ##EQU00004##
[0076] Given N.sub.R Rx antennas, signals received at the
respective Rx antennas, y.sub.1, y.sub.2, . . . , y.sub.N.sub.R may
be represented as the following vector.
y=[y.sub.1,y.sub.2, . . . ,y.sub.N.sub.R].sup.T [Equation 8]
[0077] When channels are modeled in the MIMO communication system,
they may be distinguished according to the indexes of Tx and Rx
antennas and the channel between a j.sup.th Tx antenna and an
i.sup.th Rx antenna may be represented as h.sub.ij. It is to be
noted herein that the index of the Rx antenna precedes that of the
Tx antenna in h.sub.ij.
[0078] The channels may be represented as vectors and matrices by
grouping them. Examples of vector expressions are given as below.
FIG. 3(b) illustrates channels from N.sub.T Tx antennas to an
i.sup.th Rx antenna.
[0079] As illustrated in FIG. 3(b), the channels from the N.sub.T
Tx antennas to an i.sup.th Rx antenna may be expressed as
follows.
h.sub.i.sup.T=[h.sub.i1,h.sub.i2, . . . ,h.sub.iN.sub.T] [Equation
9]
[0080] Also, all channels from the N.sub.T Tx antennas to the
N.sub.R Rx antennas may be expressed as the following matrix.
H = [ h 1 T h 2 T h i T h N R T ] = [ h 11 h 12 h 1 N T h 12 h 12 h
2 N T h i 2 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ Equation 10
] ##EQU00005##
[0081] Actual channels experience the above channel matrix H and
then are added with Additive White Gaussian Noise (AWGN). The AWGN
n.sub.1, n.sub.2, . . . , n.sub.N.sub.R added to the N.sub.R Rx
antennas is given as the following vector.
n=[n.sub.1,n.sub.2, . . . ,n.sub.N.sub.R].sup.T [Equation 11]
[0082] From the above modeled equations, the received signal can be
expressed as follows.
y = [ y 1 y 2 y i y N R ] = [ h 11 h 12 h 1 N T h 12 h 12 h 2 N T h
i 2 h i 2 h iN T h N R 1 h N R 2 h N R N T ] [ x 1 x 2 x j x N T ]
+ [ n 1 n 2 n i n N R ] = Hx + n [ Equation 12 ] ##EQU00006##
[0083] In the meantime, the numbers of rows and columns in the
channel matrix H representing channel states are determined
according to the numbers of Tx and Rx antennas. The number of rows
is identical to that of Rx antennas, N.sub.R and the number of
columns is identical to that of Tx antennas, N.sub.T in the channel
matrix H. Thus, the channel matrix H is of size
N.sub.R.times.N.sub.T. In general, the rank of a matrix is defined
as the smaller between the numbers of independent rows and columns.
Accordingly, the rank of the matrix is not larger than the number
of rows or columns. The rank of the matrix H, rank(H) is limited as
follows.
rank(H).ltoreq.min(N.sub.T,N.sub.R) [Equation 13]
[0084] As a multi-antenna transmission and reception scheme used
for operating a multi-antenna system, it may be able to use FSTD
(frequency switched transmit diversity), SFBC (Space Frequency
Block Code), STBC (Space Time Block Code), CDD (Cyclic Delay
Diversity), TSTD (time switched transmit diversity) and the like.
In a rank 2 or higher, SM (Spatial Multiplexing), GCDD (Generalized
Cyclic Delay Diversity), S-VAP (Selective Virtual Antenna
Permutation) and the like can be used.
[0085] The FSTD corresponds to a scheme of obtaining a diversity
gain by assigning a subcarrier of a different frequency to a signal
transmitted by each of multiple antennas. The SFBC corresponds to a
scheme capable of securing both a diversity gain in a corresponding
dimension and a multi-user scheduling gain by efficiently applying
selectivity in a spatial domain and a frequency domain. The STBC
corresponds to a scheme of applying selectivity in a spatial domain
and a time domain. The CDD corresponds to a scheme of obtaining a
diversity gain using path delay between transmission antennas. The
TSTD corresponds to a scheme of distinguishing signals transmitted
by multiple antennas from each other on the basis of time. The
spatial multiplexing (SM) corresponds to a scheme of increasing a
transfer rate by transmitting a different data according to an
antenna. The GCDD corresponds to a scheme of applying selectivity
in a time domain and a frequency domain. The S-VAP corresponds to a
scheme of using a single precoding matrix. The S-VAP can be
classified into an MCW (multi codeword) S-VAP for mixing multiple
codewords between antennas in spatial diversity or spatial
multiplexing and an SCW (single codeword) S-VAP for using a single
codeword.
[0086] Among the aforementioned MIMO transmission schemes, the STBC
scheme corresponds to a scheme of obtaining time diversity in a
manner that an identical data symbol is repeated in a time domain
to support orthogonality. Similarly, the SFBC scheme corresponds to
a scheme of obtaining frequency diversity in a manner that an
identical data symbol is repeated in a frequency domain to support
orthogonality. Examples of a time block code used for the STBC and
a frequency block code used for the SFBC can be represented as
equation 14 and equation 15, respectively. The equation 14
indicates a block code in case of 2 transmission antennas and the
equation 15 indicates a block code in case of 4 transmission
antennas.
1 2 ( S 1 S 2 - S 2 * S 1 * ) [ Equation 14 ] 1 2 ( S 1 S 2 0 0 0 0
S 3 S 4 - S 2 * S 1 * 0 0 0 0 - S 4 * S 3 * ) [ Equation 15 ]
##EQU00007##
[0087] In the equations 14 and 15, Si (i=1, 2, 3, 4) corresponds to
a modulated data symbol. And, in the equations 14 and 15, a row of
a matrix corresponds to an antenna port and a column of the matrix
corresponds to time (STBC) or frequency (SFBC).
[0088] Meanwhile, among the aforementioned MIMO transmission
schemes, the CDD scheme corresponds to a scheme of increasing
frequency diversity by increasing delay propagation on purpose.
FIG. 4 shows an example of a general CDD structure in a
multi-antenna system. FIG. 4 (a) shows a scheme of applying cyclic
delay in time domain. As shown in FIG. 4 (b), the CDD scheme
applying the cyclic delay of FIG. 4 (a) can also be implemented by
applying phase-shift diversity.
[0089] Codebook-Based Precoding Scheme
[0090] In order to support MIMO antenna transmission, it may be
able to apply precoding configured to appropriately distribute
transmission information to each of multiple antennas according to
a channel status and the like. A codebook-based precoding scheme
corresponds to a scheme that a transmitting end and a receiving end
determine a set of precoding matrixes in advance, the receiving end
(e.g., a UE) measures channel information from the transmitting end
(e.g., a base station) and gives feedback on a most suitable
precoding matrix (i.e., precoding matrix index (PMI) to the
transmitting end, and the transmitting end applies appropriate
precoding to signal transmission based on the PMI.
[0091] Since the codebook-based precoding scheme is a scheme of
selecting an appropriate precoding matrix from the predetermined
set of precoding matrixes, although an optimized precoding is not
always applied, feedback overhead can be reduced compared to a case
of explicitly giving feedback on optimized precoding information to
actual channel information.
[0092] FIG. 5 is a diagram for explaining a basic concept of a
codebook-based precoding.
[0093] In case of following a codebook-based precoding scheme, a
transmitting end and a receiving end share codebook information
including the prescribed number of precoding matrixes, which are
predetermined according to a transmission rank, the number of
antennas, and the like. In particular, when feedback information is
finite, the codebook-based precoding scheme can be used. The
receiving end measures a channel state via a reception signal and
may be then able to give feedback on information on the finite
number of preferred precoding matrixes (i.e., an index of a
corresponding precoding matrix) to the transmitting end based on
the aforementioned codebook information. For instance, the
receiving end measures a reception signal using ML (maximum
likelihood) or MMSE (minimum mean square error) scheme and may be
then able to select an optimized precoding matrix. Although FIG. 5
shows a case that the receiving end transmits precoding matrix
information to the transmitting end according to a codeword, by
which the present invention may be non-limited.
[0094] Having received the feedback information from the receiving
end, the transmitting end can select a specific precoding matrix
from a codebook based on the received information. The transmitting
end, which has selected the precoding matrix, performs precoding in
a manner of multiplying the number of layer signals corresponding
to a transmission rank by the selected precoding matrix and may be
then able to transmit a transmission signal on which the precoding
is performed via a plurality of antennas. In a precoding matrix,
the number of rows is identical to the number of antennas and the
number of columns is identical to a rank value. Since the rank
value is identical to the number of layers, the number of columns
is identical to the number of layers. For instance, if the number
of transmission antennas corresponds to 4 and the number of
transmission layers corresponds to 2, a precoding matrix can be
configured by a 4.times.2 matrix. Information transmitted via each
layer can be mapped to each antenna through the precoding
matrix.
[0095] Having received a signal, which is transmitted from the
transmitting end in a manner of being pre-coded, the receiving end
can restore the received signal in a manner of performing reverse
processing on the precoding processed in the transmitting end. In
general, since a precoding matrix satisfies a unitary matrix (U)
condition such as U*U.sup.H=I, the reverse processing performed on
the precoding can be performed using a scheme of multiplying
Hermite matrix (P.sup.H) of a precoding matrix (P) used in the
precoding of the transmitting end by the received signal.
[0096] For instance, Table 1 in the following shows a codebook used
for downlink transmission using 2 transmission antennas in 3GPP LTE
release-8/9 and Table 2 in the following shows a codebook used for
downlink transmission using 4 transmission antennas in 3GPP LTE
release-8/9.
TABLE-US-00001 TABLE 1 Number of rank Codebook index 1 2 0 1 2 [ 1
1 ] ##EQU00008## 1 2 [ 1 0 0 1 ] ##EQU00009## 1 1 2 [ 1 - 1 ]
##EQU00010## 1 2 [ 1 1 1 - 1 ] ##EQU00011## 2 1 2 [ 1 j ]
##EQU00012## 1 2 [ 1 1 j - j ] ##EQU00013## 3 1 2 [ 1 - j ]
##EQU00014## --
TABLE-US-00002 TABLE 2 Codebook Number of layers.sup..upsilon.
index u.sub.n 1 2 3 4 0 u.sub.0 = [1 -1 -1 -1].sup.T
W.sub.0.sup.{1} W.sub.0.sup.{14}/{square root over (2)}
W.sub.0.sup.{124}/{square root over (3)} W.sub.0.sup.{1234}/2 1
u.sub.1 = [1 -j 1 j].sup.T W.sub.1.sup.{1} W.sub.1.sup.{12}/{square
root over (2)} W.sub.1.sup.{123}/{square root over (3)}
W.sub.1.sup.{1234}/2 2 u.sub.2 = [1 1 -1 1].sup.T W.sub.2.sup.{1}
W.sub.2.sup.{12}/{square root over (2)} W.sub.2.sup.{123}/{square
root over (3)} W.sub.2.sup.{3214}/2 3 u.sub.3 = [1 j 1 -j].sup.T
W.sub.3.sup.{1} W.sub.3.sup.{12}/{square root over (2)}
W.sub.3.sup.{123}/{square root over (3)} W.sub.3.sup.{3214}/2 4
u.sub.4 = [1 (-1 - j)/{square root over (2)} -j (1 - j)/{square
root over (2)}].sup.T W.sub.4.sup.{1} W.sub.4.sup.{14}/{square root
over (2)} W.sub.4.sup.{124}/{square root over (3)}
W.sub.4.sup.{1234}/2 5 u.sub.5 = [1 (1 - j)/{square root over (2)}
j (-1 - j)/{square root over (2)}].sup.T W.sub.5.sup.{1}
W.sub.5.sup.{14}/{square root over (2)} W.sub.5.sup.{124}/{square
root over (3)} W.sub.5.sup.{1234}/2 6 u.sub.6 = [1 (1 + j)/{square
root over (2)} -j (-1 + j)/{square root over (2)}].sup.T
W.sub.6.sup.{1} W.sub.6.sup.{13}/{square root over (2)}
W.sub.6.sup.{134}/{square root over (3)} W.sub.6.sup.{1324}/2 7
u.sub.7 = [1 (-1 + j)/{square root over (2)} j (1 + j)/{square root
over (2)}].sup.T W.sub.7.sup.{1} W.sub.7.sup.{13}/{square root over
(2)} W.sub.7.sup.{134}/{square root over (3)} W.sub.7.sup.{1324}/2
8 u.sub.8 = [1 -1 1 1].sup.T W.sub.8.sup.{1}
W.sub.8.sup.{12}/{square root over (2)} W.sub.8.sup.{124}/{square
root over (3)} W.sub.8.sup.{1234}/2 9 u.sub.9 = [1 -j -1 -j].sup.T
W.sub.9.sup.{1} W.sub.9.sup.{14}/{square root over (2)}
W.sub.9.sup.{134}/{square root over (3)} W.sub.9.sup.{1234}/2 10
u.sub.10 = [1 1 1 -1].sup.T W.sub.10.sup.{1}
W.sub.10.sup.{13}/{square root over (2)} W.sub.10.sup.{123}/{square
root over (3)} W.sub.10.sup.{1324}/2 11 u.sub.11 = [1 j -1 j].sup.T
W.sub.11.sup.{1} W.sub.11.sup.{13}/{square root over (2)}
W.sub.11.sup.{134}/{square root over (3)} W.sub.11.sup.{1324}/2 12
u.sub.12 = [1 -1 -1 1].sup.T W.sub.12.sup.{1}
W.sub.12.sup.{12}/{square root over (2)} W.sub.12.sup.{123}/{square
root over (3)} W.sub.12.sup.{1234}/2 13 u.sub.13 = [1 -1 1
-1].sup.T W.sub.13.sup.{1} W.sub.13.sup.{13}/{square root over (2)}
W.sub.13.sup.{123}/{square root over (3)} W.sub.13.sup.{1324}/2 14
u.sub.14 = [1 1 -1 -1].sup.T W.sub.14.sup.{1}
W.sub.14.sup.{13}/{square root over (2)} W.sub.14.sup.{123}/{square
root over (3)} W.sub.14.sup.{3214}/2 15 u.sub.15 = [1 1 1 1].sup.T
W.sub.15.sup.{1} W.sub.15.sup.{12}/{square root over (2)}
W.sub.15.sup.{123}/{square root over (3)} W.sub.15.sup.{1234}/2
[0097] In Table 2, W.sub.n.sup.{s} can be obtained by a set {s}
configured from an equation represented as
W.sub.n=I-2u.sub.nu.sub.n.sup.H/u.sub.n.sup.Hu.sub.n. In this case,
I indicates a 4.times.4 single matrix and u.sub.n is a value given
in Table 2.
[0098] As shown in Table 1, in case of a codebook for 2
transmission antennas, it may have total 7 precoding
vectors/matrixes. In this case, since a single matrix is used for
an open-loop system, total 6 precoding vectors/matrixes are used
for a close-loop system. And, in case of a codebook for 4
transmission antennas shown in Table 2, it may have total 64
precoding vectors/matrixes.
[0099] The aforementioned codebook has a common property such as a
CM (constant modulus) property, a nested property, a constrained
alphabet property, and the like. The CM property corresponds to a
property that each element of all precoding matrixes in a codebook
does not include `0` and has a same size. The nested property
corresponds to a property that a precoding matrix of a lower rank
is configured by a subset of a specific column of a precoding
matrix of a higher rank. The constrained alphabet property
corresponds to a property that an alphabet of each element of all
precoding matrixes in a codebook is configured by
{ .+-. 1 , .+-. j , .+-. ( 1 + j ) 2 , .+-. ( - 1 + j ) 2 } .
##EQU00015##
[0100] Feedback Channel Structure
[0101] Basically, since a base station is unable to know
information on a downlink channel in FDD (frequency division
duplex) system, the base station uses channel information fed back
by a UE for downlink transmission. In case of a legacy 3GPP LTE
release-8/9 system, a UE can feedback downlink channel information
via PUCCH or PUSCH. In case of the PUCCH, the PUCCH periodically
feedbacks channel information. In case of the PUSCH, the PUSCH
aperiodically feedbacks channel information according to a request
of the base station. And, channel information can be fed back in
response to the whole of assigned frequency bands (i.e., wideband
(WB)) or the specific number of RBs (i.e., subband (SB)).
[0102] Extended Antenna Configuration
[0103] FIG. 6 is a diagram for examples of configuring 8
transmission antennas.
[0104] FIG. 6 (a) shows a case that N numbers of antennas configure
an independent channel without grouping. In general, this case is
referred to as an ULA (uniform linear array). If a plurality of
antennas are deployed in a manner of being apart from each other, a
space of a transmitter and/or a receiver may not be sufficient
enough for configuring channels independent from each other.
[0105] FIG. 6 (b) shows an antenna configuration (paired ULA) of a
ULA scheme that two antennas make a pair. In this case, an
associated channel may exist between the two antennas making a pair
and an independent channel may exist with an antenna of a different
pair.
[0106] Meanwhile, unlike a legacy 3GPP LTE release-8/9 using 4
transmission antennas in downlink, 3GPP LTE release-10 system may
use 8 transmission antennas in downlink. In order to apply the
extended antennas configuration, it is necessary to install many
antennas in an insufficient space. Hence, the ULA antenna
configurations shown in FIGS. 6 (a) and (b) may not be appropriate
for the extended configuration. Hence, as shown in FIG. 6 (c), it
may consider applying a dual-pole (or cross-pole) antenna
configuration. If transmission antennas are configured using the
dual-pole (or cross-pole) antenna configuration, although a
distance d between antennas is relatively short, it is able to
transmit data of high throughput by lowering antenna
correlation.
[0107] Codebook Structures
[0108] As mentioned in the foregoing description, if a predefined
codebook is shared between a transmitting end and receiving end, it
is able to reduce overhead of the receiving end resulted from
making a feedback on precoding information to be used for MIMO
transmission of the transmitting end. Hence, it is able to apply
efficient precoding.
[0109] As an example of configuring a predetermined codebook, it
may be able to configure a precoder matrix using a DFT (Discrete
Fourier Transform) matrix or a Walsh matrix. Or, it may be able to
configure a precoder of various forms in a manner of combining with
a phase shift matrix or a phase shift diversity matrix.
[0110] In case of a co-polarization antenna system, a codebook of a
DFT system shows good performance. In this case, when the DFT
matrix-based codebook is configured, n.times.n DFT matrix can be
defined as equation 16 in the following.
DFTn : D n ( k , ) = 1 n exp ( - j 2 .pi. k / n ) , k , = 0 , 1 , ,
n - 1 [ Equation 16 ] ##EQU00016##
[0111] The DFT matrix shown in the equation 16 exists as a single
matrix in response to a specific size n. Hence, in order to define
various precoding matrixes and appropriately use the various
precoding matrixes according to a situation, it may consider
additionally configuring and using a rotated version of a DFTn
matrix. Equation 17 in the following shows an example of a rotated
DFTn matrix.
rotated DFTn : D n ( G , g ) ( k , ) = 1 n exp ( - j 2 .pi. k ( + g
/ G ) / n ) , k , = 0 , 1 , , n - 1 , g = 0 , 1 , , G . [ Equation
17 ] ##EQU00017##
[0112] If a DFT matrix is configured using the equation 17, it may
be able to generate G number of rotated DFTn matrixes and the
generated matrixes satisfy a property of a DFT matrix.
[0113] In the following, a householder-based codebook structure is
explained. The householder-based codebook structure corresponds to
a codebook configured by a householder matrix. The householder
matrix is a matrix used for householder transform. The householder
transform is a sort of linear transformations and can be used for
performing QR decomposition. The QR decomposition is to decompose a
matrix into an orthogonal matrix (Q) and an upper triangular matrix
(R). The upper triangular matrix corresponds to a square matrix
that all components below a main diagonal line component are 0. An
example of 4.times.4 householder matrix is shown in equation 18 in
the following.
M 1 = I 4 - 2 u 0 u 1 H / u 0 2 = 1 4 * [ 1 1 1 1 1 1 - 1 - 1 1 - 1
1 - 1 1 - 1 - 1 1 ] , u 0 T = [ 1 - 1 - 1 - 1 ] [ Equation 18 ]
##EQU00018##
[0114] It may be able to generate 4.times.4 unitary matrix
including a CM property by the householder transform. Similar to a
codebook for 4 transmission antennas shown in Table 2, n.times.n
precoding matrix can be generated using the householder transform
and it may be able to configure the precoding matrix to be used for
rank transmission less than n using a column subset of the
generated precoding matrix.
[0115] Codebook for 8 Transmission Antennas
[0116] In 3GPP LTE release-10 system including an extended antenna
configuration (e.g., 8 transmission antennas), it may be able to
apply a feedback scheme previously used in a legacy 3GPP LTE
release-8/9 system in a manner of extending the feedback scheme.
For example, it may be able to feedback such channel state
information (CSI) as an RI (rank indicator), a PMI (precoding
matrix index), CQI (channel quality information) and the like. In
the following, a method of designing a dual precoder-based feedback
codebook capable of being used in a system supporting an extended
antenna configuration is explained. In order to indicate a precoder
to be used for MIMO transmission of a transmitting end in the dual
precoder-based feedback codebook, a receiving end can transmit a
precoding matrix index to the transmitting end. A precoding matrix
can be indicated by a combination of two PMIs different from each
other. In particular, if the receiving end feedbacks the two PMIs
different from each other (i.e., a first PMI and a second PMI) to
the transmitting end, the transmitting end determines a precoding
matrix indicated by the first and the second PMI and may be then
able to apply the determined precoding matrix to MIMO
transmission.
[0117] In designing the dual precoder-based feedback codebook, it
may consider MIMO transmission transmitted by 8 transmission
antennas, whether or not single user-MIMO (SU-MIMO) and multiple
user-MIMO (MU-MIMO) are supported, suitability of various antenna
configurations, a reference of codebook design, a size of a
codebook, and the like.
[0118] When a codebook is applied to MIMO transmission transmitted
by 8 transmission antennas, if the codebook is greater than rank 2,
SU-MIMO is supported only. If the codebook is equal to or less than
the rank 2, it may consider designing a feedback codebook optimized
to both the SU-MIMO and the MU-MIMO and the feedback codebook
appropriate for various antenna configurations.
[0119] Regarding the MU-MIMO, it may be preferable to make UEs
participating in the MU-MIMO to be separated from each other in a
correlation domain. Hence, it is necessary to design a codebook for
the MU-MIMO to be properly operated on a channel of high
correlation. Since DFT vectors provide good performance on the
channel of high correlation, it may consider including a DFT vector
in a set of codebooks up to rank-2. And, in high scattering
propagation environment (e.g., indoor environment including many
reflected waves) capable of generating many spatial channels, a
SU-MIMO operation may be more suitable as a MIMO transmission
scheme. Hence, it may be able to configure a codebook for a rank
greater than rank-2 to have good performance of identifying
multiple layers.
[0120] When a precoder for MIMO transmission is designed, it may be
preferable to make a precoder structure have good performance in
response to various antenna configurations (low correlation, high
correlation, cross-polarization, and the like). In case of
arranging 8 transmission antennas, it may be able to configure a
cross-polarization array including 4.lamda. antenna space as a
low-correlation antenna configuration, a ULA including 0.5.lamda.
antenna space as a high-correlation antenna configuration, or a
cross-polarization array including 0.5.lamda. antenna space as a
cross-polarization antenna configuration. A DFT-based codebook
structure can provide good performance in response to the
high-correlation antenna configuration.
[0121] Meanwhile, block diagonal matrixes may be more suitable for
the cross-polarization antenna configuration. Hence, if a diagonal
matrix is introduced to a codebook for 8 transmission antennas, it
is able to configure a codebook capable of providing goof
performance to all antenna configurations.
[0122] As mentioned in the foregoing description, a reference of
codebook design is to satisfy a unitary codebook, a CM property, a
constrained alphabet property, an appropriate codebook size, a
nested property and the like. The reference is applied to 3GPP LTE
release-8/9 codebook design. It may consider applying the reference
of codebook design to 3GPP LTE release-10 codebook design
supporting an extended antenna configuration as well.
[0123] In relation to a size of a codebook, in order to
sufficiently support a merit of using 8 transmission antennas, it
is necessary to increase the size of the codebook. In order to
obtain a sufficient precoding gain from the 8 transmission antennas
in low correlation environment, a codebook (e.g., a codebook of a
size greater than 4 bits in response to a rank 1 and a rank 2) of a
big size may be required. A codebook of a size of 4 bits may be
sufficient in obtaining a precoding gain in high correlation
environment. Yet, in order to achieve a multiplexing gain of the
MU-MIMO, it may be able to increase a codebook size for the rank 1
and the rank 2.
[0124] Based on the aforementioned contents, the present invention
proposes a method transmitting a reference signal in a wireless
communication system. In particular, the present invention is
effective when a transmitting end uses a 3D MIMO system utilizing
2D-array antenna that a horizontal antenna and a vertical antenna
are installed together. As a representative embodiment, the present
invention can be utilized for downlink communication between a base
station and a user equipment in a cellular network.
[0125] In a system appearing after LTE Rel-12, using an antenna
system utilizing AAS is considered. It is expected that the AAS is
able to actively control overall antenna beam pattern by changing a
beam pattern of each antenna compared to a previous passive antenna
system. Since the control of the antenna beam pattern is able to
reduce interference or increase a channel gain, thereby increasing
overall system performance. If the AAS is constructed in 2
dimensions (2D-AAS), it is able to more efficiently (in 3D) control
a main lobe of an antenna in the aspect of an antenna pattern and
it is able to more actively change a transmission beam according to
a location of a receiver.
[0126] FIG. 7 shows an example of the aforementioned 2D-AAS. As
shown in FIG. 7, the 2D-AAS installs antennas in vertical and
horizontal directions to install a system of a plurality of
antennas.
[0127] Moreover, in order to perform beamforming for the 2D-AAS, as
shown in FIG. 8, it is preferable to configure a single radio
frequency (RF) chain per antenna element. FIG. 8 shows a case that
32 antennas in total are configured by installing 4 antenna
elements in horizontal direction and installing 8 antenna elements
in vertical direction.
[0128] However, when multiple antenna elements are installed in a
communication system, if RF chains as many as the number of the
multiple antenna elements are installed, a cost issue may occur. In
consideration of the cost issue, as shown in FIG. 9, many
communication systems connect a plurality of antenna elements to a
single RF chain using a phase shifter to make a baseband signal
passed through the RF chain to be precoded by the phase
shifter.
[0129] FIG. 9 is explained in more detail. Referring to FIG. 9, the
number of antenna elements is 32 in total in a manner that 4
antenna elements are configured in horizontal direction and 8
antenna elements are configured in vertical direction. 8 antenna
elements in each vertical direction are connected with a single RF
chain through a phase shifter.
[0130] Hence, in FIG. 9, antenna beam control in horizontal
direction can be precoded by an RF chain and antenna beam control
in vertical direction can be precoded by a phase shifter. The
antenna beam control in horizontal direction can be performed
through an RF chain in every different frequency resource at the
same time. In other word, it may be able to generate 4 horizontal
beam directions in every different frequency resource at the same
time.
[0131] Yet, the antenna beam control in vertical direction is not
the same. Assume that 4 beams in vertical direction are generated
through a phase shifter in a random frequency resource at a certain
time. In this case, it is difficult to generate a beam rather than
the 4 beams in vertical direction in a different frequency resource
at the same time.
[0132] In other word, when 8 antenna elements in vertical direction
connected with each RF chain are precoded by a phase shifter, the
precoding is applied to all frequency resources at the same
time.
[0133] Although vertical precoding, which is generated by a phase
shifter at the same time, is identically applied to the whole
frequency, it may be able to generate a new vertical precoding in a
different time resource through the phase shifter. Hence, a part to
which restrictive precoding is applied in a beam is mainly
considered as a frequency domain.
[0134] In LTE system, as a representative signal for downlink,
there are 3 types of signals including a CSI-RS, a DM-RS, and a CRS
and channels including PDCCH corresponding to a control channel and
PDSCH on which data is transmitted. The CSI-RS is used for the
usage of channel estimation by a UE to calculate CSI and the DM-RS
is used for estimating a channel by a UE to demodulate data. A UE
uses the CRS to calculate CSI or estimate a channel for data
demodulation. The UE uses the CRS to measure RSRP (received signal
received power). The RSs, the PDCCH, and the PDSCH are transmitted
through a port of 3 types. The CSI-RS is transmitted through a
CSI-RS port. The DRMS is transmitted through a DMRS port. The CRS
and the PDCCH are transmitted through a CRS port. The PDSCH is
transmitted through a CRS port or a DMRS port according to a
transmission mode.
[0135] A location at which each of the RSs, the PDCCH, and the
PDSCH is transmitted is differently classified in a frequency
resource and a time resource. Yet, in the aspect of the same time
resource, there exists a case that a plurality of RSs are
transmitted together. Assume that a base station including the
antenna system shown in FIG. 9 transmits data on PDSCH while
transmitting a DMRS using 4-port DMRS. In this case, assume that a
CSI-RS is transmitted to a different frequency resource in a time
resource in which the 4-port DMRS and the PDSCH are transmitted.
Yet, as mentioned in the foregoing description, it is difficult to
apply a beam direction rather than a beam in vertical direction
applied to the 4-port DMRS to the CSI-RS. Since a beam direction
applied to DMRS corresponds to specific beams for a specific UE, a
vertical direction of specific directions is applied. Hence, it is
very difficult to generate a beam in vertical direction commonly
used in the CSI-RS.
[0136] Method 1
[0137] In order to more freely control a passively generated beam
in the 3D-MIMO scenario, the present invention proposes to install
RF chains different from each other according to a CSI-RS port, a
DMRS port, and a CRS port corresponding to 3 RS ports mainly used
for downlink transmission in accordance with a method 1-A or a
method 1-B described in the following.
[0138] Method 1-A:
[0139] While RF chains for a CSI-RS port, a DMRS port, and a CRS
port are installed, a different RF chain is installed according to
each RS type (CSI-RS, DMRS, and CRS). Each RF chain is connected
with one or more antenna elements through a phase shifter.
[0140] The method 1-A is explained in detail with reference to FIG.
10 in the following. Referring to FIG. 10, there are 32 antenna
elements in total in a manner that 4 antenna elements are
configured in horizontal direction and 8 antenna elements are
configured in vertical direction. Each RF chain is connected with
the 8 antenna elements in vertical direction through 8 phase
shifters.
[0141] In FIG. 10, the number of RF chains corresponds to 10. In
this case, 4 RF chains are used for a DMRS port, another 4 RF
chains are used for a CSI-RS port, and the remaining 2 RF chains
are used for a CRS port. Yet, if it is assumed that a power
amplifier is attached to every RF chain, it is necessary to
increase capacity of a power amplifier attached to an RF chain for
a CRS port when the CRS port is configured by 2 RF chains. Hence,
the RF chain for the CRS port can also be managed by the number of
RF chains identical to the number of RF chains for the DMRS port
and the CSI-RS port.
[0142] Method 1-B:
[0143] Yet, in case of an RS port managed in a current LTE system,
a CRS port and a CSI-RS port are transmitted from a different time
resource in most case. (Since PDSCH transmitted through a CRS port
in a partial transmission mode can be transmitted from a time
resource in which a CSI-RS is transmitted, method 1-B can be
restrictively managed compared to the method 1-A.)
[0144] Hence, although the same RF chain is used for the CRS port
and the CSI-RS port, restriction on a beam is trivial. Based on
this, it may be able to modify and use the method 1-A. When RF
chains are installed for a CSI-RS port, a DMRS port, and a CS port,
the RF chains for the DMRS port differ from the RF chains for the
CSI-RS port. On the contrary, the RF chains for the CSI-RS port can
also be used for the CRS port.
[0145] Each RF chain is connected with one or more antenna elements
through a phase shifter. The method 1-B is explained with reference
to FIG. 11. Referring to FIG. 11, there are 64 antenna elements in
total in a manner that 4 antenna elements are configured in
horizontal direction and 8 antenna elements are configured in
vertical direction. And, each RF chain is connected with the 8
antenna elements in vertical direction through 8 phase shifters. In
FIG. 11, the number of RF chains corresponds to 8. In this case, 4
RF chains are used for the DMRS port and another 4 RF chains are
used for the CSI-RS port and the CRS port.
[0146] Method 2
[0147] In the following, a method of configuring a CSI-RS in a
system having RF chains less than the total number of antenna
elements and a CSI-RS design are described.
[0148] First of all, a CSI-RS currently used in LTE is explained.
Currently, a modulated symbol of a CSI-RS is determined by equation
19 described in the following.
a.sub.k,l.sup.(p)=w.sub.l''r.sub.l,n.sub.s(m') [Equation 19]
[0149] In equation 19, r.sub.l,n.sub.s(m) becomes an RS sequence
value of an m.sup.th resource block (RB) in an l.sup.th OFDM symbol
in an n.sub.S slot and w.sub.l'' becomes a value of 1 or -1 for
performing CDM in a sequence value. And, a.sub.k,l.sup.(p) may
correspond to a modulated symbol in a resource element (RE) having
a position of an l.sup.th OFDM symbol at k.sup.th frequency
position at a p.sup.th port. In this case, resource mapping of a
CSI-RS can be determined by equations 19 and 20 described in the
following.
k = k ' + 12 m + { - 0 for p .di-elect cons. { 15 , 16 } , normal
cyclic prefix - 6 for p .di-elect cons. { 17 , 18 } , normal cyclic
prefix - 1 for p .di-elect cons. { 19 , 20 } , normal cyclic prefix
- 7 for p .di-elect cons. { 21 , 22 } , normal cyclic prefix - 0
for p .di-elect cons. { 15 , 16 } , extended cyclic prefix - 3 for
p .di-elect cons. { 17 , 18 } , extended cyclic prefix - 6 for p
.di-elect cons. { 19 , 20 } , extended cyclic prefix - 9 for p
.di-elect cons. { 21 , 22 } , extended cyclic prefix l = l ' + { l
'' CSI reference signal configurations 0 - 19 , normal cyclic
prefix 2 l '' CSI reference signal configurations 20 - 31 , normal
cyclic prefix l '' CSI reference signal configurations 0 - 27 ,
extended cyclic prefix w l ' = { 1 p .di-elect cons. { 15 , 17 , 19
, 21 } ( - 1 ) l '' p .di-elect cons. { 16 , 18 , 20 , 22 } l '' =
0 , 1 m = 0 , 1 , , N RB DL - 1 m ' = m + N RB max , DL - N RB DL 2
[ Equation 20 ] ##EQU00019##
[0150] In the equation 20, N.sub.RB.sup.max,DL corresponds to a
maximum bandwidth capable of being possessed by a system and
N.sub.RB.sup.DL corresponds to a bandwidth of a current system. In
the equation 20, values (k',l') for resource mapping and a slot
condition related to the values are shown in Tables 3 and 4. Table
3 corresponds to a table for a normal CP and Table 4 corresponds to
a table for an extended CP.
TABLE-US-00003 TABLE 3 Number of CSI reference signals configured
CSI refer- 1 or 2 4 8 ence sig- n.sub.s n.sub.s n.sub.s nal con-
mod mod mod figuration (k', l') 2 (k', l') 2 (k', l') 2 Frame 0 (9,
5) 0 (9, 5) 0 (9, 5) 0 struc- 1 (11, 2) 1 (11, 2) 1 (11, 2) 1 ture
2 (9, 2) 1 (9, 2) 1 (9, 2) 1 type 1 3 (7, 2) 1 (7, 2) 1 (7, 2) 1
and 2 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 0 6 (10, 2) 1
(10, 2) 1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5) 1 (8, 5)
1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15
(2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20
(11, 1) 1 (11, 1) 1 (11, 1) 1 struc- 21 (9, 1) 1 (9, 1) 1 (9, 1) 1
ture 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 type 2 23 (10, 1) 1 (10, 1) 1
only 24 (8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4,
1) 1 28 (3, 1) 1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1
TABLE-US-00004 TABLE 4 Number of CSI reference signals configured
CSI refer- 1 or 2 4 8 ence sig- n.sub.s n.sub.s n.sub.s nal con-
mod mod mod figuration (k', l') 2 (k', l') 2 (k', l') 2 Frame 0
(11, 4) 0 (11, 4) 0 (11, 4) 0 struc- 1 (9, 4) 0 (9, 4) 0 (9, 4) 0
ture 2 (10, 4) 1 (10, 4) 1 (10, 4) 1 type 1 3 (9, 4) 1 (9, 4) 1 (9,
4) 1 and 2 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6 (4, 4) 1 (4,
4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 0 11 (0,
4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Frame 16 (11,
1) 1 (11, 1) 1 (11, 1) 1 struc- 17 (10, 1) 1 (10, 1) 1 (10, 1) 1
ture 18 (9, 1) 1 (9, 1) 1 (9, 1) 1 type 2 19 (5, 1) 1 (5, 1) 1 only
20 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1
24 (6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1
[0151] A CSI-RS mapping characteristic in a normal CP is explained
in the following. 2-port CSI-RS is positioned at 2 REs over 2
adjacent OFDM symbols per PRB pair and the 2 REs are located at the
same frequency resource. 4-port CSI-RS is positioned at 4 REs over
2 adjacent OFDM symbols per PRB pair and each of the 2 REs is
located at the same frequency resource. 8-port CSI-RS is positioned
at 8 REs over 2 adjacent OFDM symbols per PRB pair and each of the
2 REs is located at the same frequency resource. This can be
schematized via FIG. 12.
[0152] Referring to FIG. 12, all CSI-RS structures are located over
2 adjacent OFDM symbols and frequency resources are located at the
same position by two. In case of two symbols located at the same
frequency resource of two adjacent OFDM symbols, CDM is applied to
the two symbols as [1 1] and [1 -1].
[0153] As mentioned in the foregoing description, when the total
number of antenna elements is smaller than the total number of RF
chains, there exists a limit in generating a different beam in a
different frequency resource at the same time.
[0154] However, according to a CSI-RS structure of current LTE, it
may have a situation that a half of beams are shown only due to a
CDM structure.
[0155] For example, assume that a base station has an antenna
system shown in FIG. 11. In this case, the base station can
generate 4 beams at a time using an RF chain for a CSI-RS for beams
in vertical direction. In this case, if the base station intends to
show 8 different beams to UEs via 8-port CSI-RS to know the beam in
vertical direction, current LTE system is unable to do it. This is
because, as shown in FIG. 12, since the 8-port CSI-RS is located at
4 REs per one OFDM symbol but CDM is applied to an adjacent OFDM
symbol, it is necessary to generate 8 beams per one symbol.
[0156] In order to solve a problem that it is unable to freely
transmit a beam in a CSI-RS to which FDM, TDM, and CDM are applied
at the same time, the present invention proposes to indicate that
FDM and TDM are applied only and CDM is not applied when the CSI-RS
is configured. Or, if the indication does not exist, it may follow
a specific CSI-RS configuration that applies FDM and TDM only
without CDM.
[0157] While using the CSI-RS resource mapping of the current LTE
system (equation 19, equation 20, Table 3-1, and Table 3-2), CSI-RS
configuration may indicate whether or not CDM is used by 1 bit. (A
specific CSI-RS configuration may follow a configuration of
applying FDM and TDM all the time while not applying CDM without
the 1-bit indication.)
[0158] Method 2-A:
[0159] When a CSI-RS is configured, if it is indicated that FDM and
TDM are applied only without applying CDM, a base station transmits
a CSI-RS under an assumption that
w l '' = { 1 p .di-elect cons. { 15 , 17 , 19 , 21 } ( - 1 ) l '' p
.di-elect cons. { 16 , 18 , 20 , 22 } l '' = 0 , 1 ##EQU00020##
of equation 20 is modified into equation 21 in the following. A UE
can perform channel estimation using the CSI-RS through the
modified equation 21.
w l '' = 1 l '' = { 0 p .di-elect cons. { 15 , 17 , 19 , 21 } 1 p
.di-elect cons. { 16 , 18 , 20 , 22 } [ Equation 21 ]
##EQU00021##
[0160] FIG. 13 is a diagram for a case of performing
transmission/mapping by modifying a CSI-RS according to the method
2-A of the present invention.
[0161] Method 2-B:
[0162] Alternately, as a different method, when N-port CSI-RS
resource mapping is performed, the present invention proposes to
map a CSI-RS over 4 OFDM symbols instead of 2 OFDM symbols.
[0163] According to a current LTE system (equation 19, equation 20,
Table A, and Table 4) CSI-RS resource mapping, 2 CSI-RSs having the
same port number and are mapped to a different OFDM symbol are
bound. And, when a port of each of the CSI-RSs is represented as
{15-1, 16-1, 17-1, 18-1, 19-1, 20-1, 21-1, 22-1} and {15-2, 16-2,
17-2, 18-2, 19-2, 20-2, 21-2, 22-2} (in this case, 15-1 corresponds
to a first CSI-RS mapped to a port 15 and 15-2 corresponds to a
second CSI-RS mapped to the port 15), {15-1, 16-1, 17-1, 18-1} and
{19-2, 20-2, 21-2, 22-2} ports are maintained as it is, but {19-1,
20-1, 21-1, 22-1} and {15-2, 16-2, 17-2, 18-2} ports are exchanged
with each other by 1:1. (For example, 21-1 is exchanged with 17-2
and 17-2 is exchanged with 21-1).
[0164] In this case, when two CSI-RSs mapped to a different OFDM
symbol are bound, a base station and a UE can promise the two
CSI-RSs to be bound in advance. When a CSI-RS is configured, it may
indicate whether to apply the method 2-B using 1 bit.
[0165] Method 3
[0166] As a further different method of the present invention,
according to a current LTE system (equation 19, equation 20, Table
3, and Table 4) CSI-RS resource mapping, N.sub.2 number of 2-port
CSI-RSs, which are mapped to a different OFDM symbol, are bound to
make 2N.sub.2-port CSI-RSs. When a CSI-RS is configured, it may
indicate whether to apply the method 3 using 1 bit.
[0167] In the present invention, the aforementioned methods 2 and 3
can be used in a manner of being combined with each other.
[0168] The above-described embodiments correspond to combinations
of elements and features of the present invention in prescribed
forms. And, the respective elements or features may be considered
as selective unless they are explicitly mentioned. Each of the
elements or features can be implemented in a form failing to be
combined with other elements or features. Moreover, it is able to
implement an embodiment of the present invention by combining
elements and/or features together in part. A sequence of operations
explained for each embodiment of the present invention can be
modified. Some configurations or features of one embodiment can be
included in another embodiment or can be substituted for
corresponding configurations or features of another embodiment.
And, it is apparently understandable that an embodiment is
configured by combining claims failing to have relation of explicit
citation in the appended claims together or can be included as new
claims by amendment after filing an application.
[0169] In this disclosure, a specific operation explained as
performed by a base station may be performed by an upper node of
the base station in some cases. In particular, in a network
constructed with a plurality of network nodes including a base
station, it is apparent that various operations performed for
communication with a user equipment can be performed by a base
station or other networks except the base station. `Base station
(BS)` may be substituted with such a terminology as a fixed
station, a Node B, an eNode B (eNB), an access point (AP) and the
like.
[0170] Embodiments of the present invention can be implemented
using various means. For instance, embodiments of the present
invention can be implemented using hardware, firmware, software
and/or any combinations thereof. In the implementation by hardware,
a method according to each embodiment of the present invention can
be implemented by at least one selected from the group consisting
of ASICs (application specific integrated circuits), DSPs (digital
signal processors), DSPDs (digital signal processing devices), PLDs
(programmable logic devices), FPGAs (field programmable gate
arrays), processor, controller, microcontroller, microprocessor and
the like.
[0171] In case of the implementation by firmware or software, a
method according to each embodiment of the present invention can be
implemented by modules, procedures, and/or functions for performing
the above-explained functions or operations. Software code is
stored in a memory unit and is then drivable by a processor.
[0172] The memory unit is provided within or outside the processor
to exchange data with the processor through the various means known
in public.
[0173] While the present invention has been described and
illustrated herein with reference to the preferred embodiments
thereof, it will be apparent to those skilled in the art that
various modifications and variations can be made therein without
departing from the spirit and scope of the invention. Thus, it is
intended that the present invention covers the modifications and
variations of this invention that come within the scope of the
appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
[0174] Although the method of transmitting a reference signal in a
multi-antenna wireless communication system and an apparatus
therefor are described centering on examples applied to 3GPP LTE
system, it may be applicable to various wireless communication
systems as well as to the 3GPP LTE system.
* * * * *